In recent years, contrast-enhanced ultrasonography has been conducted for benignancy and malignancy differentiation of a tumor. The contrast-enhanced ultrasonography is one of the image diagnosis methods for tumor characterization. The contrast-enhanced ultrasonography determines tumor grade by administering an ultrasound contrast agent having bubbles as a main component into the blood flow, and obtaining using an ultrasound diagnostic apparatus (for example, see FIG. 11) the images of the ultrasound contrast agent together with tissue of a subject as a video.
One of the analysis methods of tumor characterization is a diagnostic method based on a time intensity curve (TIC) shown in FIG. 6. The TIC is used to analyze a change in intensity over time observed in the site of interest. Research has been conducted for applying the TIC for malignancy grading of a tumor (Non-patent Literature 1).
Furthermore, recent years have seen studies for malignancy grading of a tumor based on a micro-vessel pattern in a tumor, by using the ultrasound contrast agent (Non-patent Literature 2). The micro-vessel pattern is represented as an image with a technique called a maximum intensity holding. As shown in FIG. 5, in the maximum intensity holding, each of bubbles of the ultrasound contrast agent passing through a microvessel appears on the image as a dot having high-intensity. The micro-vessel pattern is constructed by sequentially adding the intensities (Patent Literature 1). The maximum intensity holding is used in combination with destruction of the ultrasound contrast agent. Such a method is referred to as a flash replenishment imaging (FRI). In the FRI, ultrasound having a high sound pressure is transmitted to destroy the ultrasound contrast agent, and the ultrasound contrast agent flowing into the site of interest again is observed by a maximum intensity holding. With this, the flow of the ultrasound contrast agent can be repeatedly observed without administrating the ultrasound contrast agent to the subject again.